1. Field of the Invention
This invention relates to a system for patterning a lapping surface of a polishing tool.
2. Description of Related Art
Continuous polishing (xe2x80x9cCPxe2x80x9d) machines have been used to polish workpieces to provide the workpieces with extremely flat surfaces. A typical CP machine may have an annular lapping table with an inner diameter of approximately 16 inches and an outer diameter of approximately 50 to 60 inches. For the polishing of optical substrates formed of, for example, borosilicate crown optical glass or fused silica, pitch is melted and poured onto the surface of the lapping table. The pitch is a viscous tar-like substance that serves as a carrier for a polishing agent, such as zirconia or cerium oxide. When coated onto the lapping table, the pitch forms a hard lapping surface for polishing the face of the workpiece. Various forms of coating substances are well-known to those of ordinary skill in the art, and one exemplary pitch is Gugolz #73 or #82. The Gugolz pitch can be melted and then poured over the lapping table as the table is rotated to form an even lapping surface. After cooling, the pitch solidifies to form a hard lapping surface.
A slurry, such as a distilled water and cerium oxide compound, is deposited onto the lapping surface during polishing. Each workpiece is captured in position by a septum, and a downforce can be applied on the backside of the workpiece to press the front face against the rotating lapping surface. The septum is held within a rotating ring, enabling the workpieces to rotate within the ring over the lapping surface.
In order to facilitate good slurry distribution and to prevent hydroplaning of the workpiece, grooves may be cut into the hard lapping surface. One method for providing these grooves is to draw a single point tool or a rotating drill bit along the lapping surface in a radial direction and/or rotate the lapping surface. However, the lapping tool may not provide precise control over the rotation of the platen and the movement of the cutting tool may generally be controlled in the radial direction alone. This method can be used to produce grooves in circular, spiral, or radial patterns on the lapping surface, but other types of patterns are difficult or impossible to produce. In addition, the polishing of substrates using a lapping surface patterned with such groove patterns may produce poor results.
In another method for patterning the lapping surface, an operator will manually pull a band saw blade across the lapping surface to create a first set of parallel grooves in the lapping surface. Then, the operator cuts another set of parallel grooves at some angle to the first set to create a cross-hatch groove pattern on the lapping surface. There are numerous problems associated with this method. First, the manual cutting of the grooves does not provide consistent results and depends heavily on the skill and performance of the operator. The angle the blade is held, the pressure applied, and the precision of the groove placement all affect the final pattern. In addition, the process is not ergonomically safe because for large lapping surfaces, the operator must reach outward from the waist level at distances of over 30 inches while engaging in repetitive motion. Another disadvantage of this process is that the cutting is time consuming, resulting in significant tool down times when the lapping surface must be re-patterned. Yet another disadvantage is that the drawing of a blade across the lapping surface produces flakes of pitch material, which creates sticky dust particles. These particles are time consuming to clean and may pose a health hazard if inhaled by the operator.
Accordingly, there is a need for an improved lapping surface patterning system which efficiently produces consistent patterns on the lapping surface.
In accordance with the invention, a system is provided for patterning a lapping surface on a lapping tool, said lapping surface having a circular inner diameter and a circular outer diameter. The system comprises: an outer support mounted on the lapping tool; a radial arm having an inner end rotatably supported at an axis of rotation located within the inner diameter of the lapping surface and an outer end movably supported by said outer support such that said radial arm is rotatable about the axis of rotation; a cutting tool mounted on the radial arm for movement from the inner diameter of the lapping surface to the outer diameter of the lapping surface; a radial positioning motor for positioning the cutting tool at a plurality of locations between the inner diameter of the lapping surface and the outer diameter of the lapping surface; and an angular positioning motor for rotating the radial arm about the axis of rotation to position the radial arm at a plurality of angular locations.
In accordance with another aspect of the present invention, a system is provided for patterning a lapping surface on a lapping tool, said lapping surface having a circular inner diameter and a circular outer diameter. The system comprises a patterning apparatus and a motion controller. The patterning apparatus comprises: an outer support mounted on the lapping tool; a radial arm having an inner end rotatably supported at an axis of rotation located within the inner diameter of the lapping surface and an outer end movably supported by said outer support such that said radial arm is rotatable about the axis of rotation; an angular positioning motor for rotating the radial arm about the axis of rotation to position the radial arm at a plurality of angular locations; a cutting tool mounted on the radial arm for movement from the inner diameter of the lapping surface to the outer diameter of the lapping surface; and a radial positioning motor for positioning the cutting tool at a plurality of locations between the inner diameter of the lapping surface and the outer diameter of the lapping surface. The motion controller comprises: a position memory for storing radial position information and angular position information; and a motor interface connecting the position memory with the radial positioning motor and the angular positioning motor to transmit the radial position information to the radial positioning motor and the angular position information to the angular positioning motor.
In accordance with another aspect of the present invention, a method is provided for patterning a lapping surface on a lapping tool, said lapping surface having a circular inner diameter and a circular outer diameter. The method comprises: positioning a patterning apparatus over the lapping surface, said patterning apparatus comprising an outer support mounted on the lapping tool, a radial arm having an inner end rotatably supported at an axis of rotation located within the inner diameter of the lapping surface and an outer end movably supported by said outer support, and a cutting tool mounted on the radial arm for movement from the inner diameter of the lapping surface to the outer diameter of the lapping surface; storing pattern information in a motion controller memory; transmitting control information to a radial positioning motor for positioning the cutting tool along the radial arm and to an angular positioning motor for rotating the radial arm about the axis of rotation, said control information corresponding to said pattern information in the motion controller memory; and operating said cutting tool to form grooves in the lapping surface corresponding to the pattern information.